1. Field of the Invention
The present invention relates to door lock devices and more particularly to a safety device of a door lock for locking a double-swinging type fire protection door.
2. Background Art
FIGS. 1 and 2 of the drawings show a door lock for locking a double-swinging type fire protection door according to the prior art. The door lock includes a sliding rod 6' having one end coupled to a lock bolt 61' and an opposite end connected to a spring 60'. An actuating rod 5' which is surrounded by a coil spring 50' is coupled at one end thereof to the sliding rod 6' by a link 4' and connected at the opposite end to a cam 9'. A latch bolt 8' extends out of the casing of the door lock and cooperates with the cam 9'. When the double-swinging door is closed, the latch bolt 8' is pushed inside the casing of the door lock causing the cam 9' to move the sliding rod 6' upwardly via the actuating rod 5' and the link 4'. Accordingly, the lock bolt 61' is extended out of the casing of the door lock with the upward movement of the sliding rod 6' and inserted into the usual hole on the frame of the door to lock the door in the locked position.
Although this conventional door lock is functional under normal conditions, it has several drawbacks. First, the aforesaid door lock is complicated in structure and in assembly process, and, consequently, its manufacturing cost is high. Another drawback to this door lock is that the springs (50' and 60') may be subject to deformation and damage under heat during a fire thereby preventing the locking mechanism from functioning in a normal manner to insure that the lock bolt 61' can be moved upwards to the locked position of FIG. 2. Consequently, the door may remain unlocked and fail to prevent the spread of the fire.